The present invention relates to embossed sheet forming apparatuses and related rotary phase difference control methods and, more particularly, to an embossed sheet forming apparatus and a related rotary phase difference control method for forming an optical high-precision both-sided embossed sheet.
An optical high-precision both-sided embossed sheet such as a lenticular sheet for use in a rear projector screen has front and rear surfaces, both of which are formed with embossed patterns. Such a both-sided embossed sheet is, as disclosed in Japanese Patent Provisional Publication No. 2004-142182, formed by an extrusion molding method using an embossed sheet forming apparatus. This embossed sheet forming apparatus includes two embossing rollers, having outer peripheries engraved with patterns, which are juxtaposed in parallel with each other.
The embossed sheet forming apparatus has issues as follows: When the embossed sheet forming apparatus is continuously operated, since the respective rolling speeds of the two embossing rollers are fluctuated, the speed ratio (draw ratio) of the two embossing rollers is also fluctuated. Consequently, the rotary phase difference of the two embossing rollers is fluctuated. The fluctuation of such a rotary phase difference (rotary phase deviation), as shown in FIG. 1A, causes swell-like deviation (embossing phase deviation) to occur in the embossing phase difference of front and rear surfaces of the both-sided embossed sheet along a roller axis direction (sheet width direction).
In FIG. 1A, “LPs1” denotes the embossing phase of the front surface of the both-sided embossed sheet in a roller axis direction; “LPs2” the embossing phase of the rear surface of the both-sided embossed sheet in the roller axis direction; and “A” the phase difference of the phases LPs1 and LPs2. The phase difference A shows that it cyclically and widely fluctuates the embossing phase deviation of the front and rear surfaces along the roller axis direction (sheet width direction).
This embossed sheet forming apparatus therefore faces a difficulty in forming a both-sided high-precision embossed sheet that the embossing phase deviation of the front and rear surfaces falls within a tolerance.